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NAME
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parsehtml, printitems, validitems, freeitems, freedocinfo, dimenkind,
dimenspec, targetid, targetname, fromStr, toStr – HTML parser
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SYNOPSIS
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#include <u.h>
#include <libc.h>
#include <html.h>
Item* parsehtml(uchar* data, int datalen, Rune* src, int mtype,
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int chset, Docinfo** pdi)
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void printitems(Item* items, char* msg)
int validitems(Item* items)
void freeitems(Item* items)
void freedocinfo(Docinfo* d)
int dimenkind(Dimen d)
int dimenspec(Dimen d)
int targetid(Rune* s)
Rune* targetname(int targid)
uchar* fromStr(Rune* buf, int n, int chset)
Rune* toStr(uchar* buf, int n, int chset)
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DESCRIPTION
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This library implements a parser for HTML 4.0 documents. The parsed
HTML is converted into an intermediate representation that describes
how the formatted HTML should be laid out.
Parsehtml parses an entire HTML document contained in the buffer
data and having length datalen. The URL of the document should
be passed in as src. Mtype is the media type of the document,
which should be either TextHtml or TextPlain. The character set
of the document is described in chset, which can be one of US_Ascii,
ISO_8859_1,
UTF_8 or Unicode. The return value is a linked list of Item structures,
described in detail below. As a side effect, *pdi is set to point
to a newly created Docinfo structure, containing information pertaining
to the entire document.
The library expects two allocation routines to be provided by
the caller, emalloc and erealloc. These routines are analogous
to the standard malloc and realloc routines, except that they
should not return if the memory allocation fails. In addition,
emalloc is required to zero the memory.
For debugging purposes, printitems may be called to display the
contents of an item list; individual items may be printed using
the %I print verb, installed on the first call to parsehtml. validitems
traverses the item list, checking that all of the pointers are
valid. It returns 1 is everything is ok, and 0 if an error was
found. Normally, one would not call these
routines directly. Instead, one sets the global variable dbgbuild
and the library calls them automatically. One can also set warn,
to cause the library to print a warning whenever it finds a problem
with the input document, and dbglex, to print debugging information
in the lexer.
When an item list is finished with, it should be freed with freeitems.
Then, freedocinfo should be called on the pointer returned in
*pdi.
Dimenkind and dimenspec are provided to interpret the Dimen type,
as described in the section Dimension Specifications.
Frame target names are mapped to integer ids via a global, permanent
mapping. To find the value for a given name, call targetid, which
allocates a new id if the name hasn’t been seen before. The name
of a given, known id may be retrieved using targetname. The library
predefines FTtop, FTself, FTparent and FTblank.
The library handles all text as Unicode strings (type Rune*).
Character set conversion is provided by fromStr and toStr. FromStr
takes n Unicode characters from buf and converts them to the character
set described by chset. ToStr takes n bytes from buf, interpretted
as belonging to character set chset, and converts them to a Unicode
string. Both
routines null-terminate the result, and use emalloc to allocate
space for it.
Items
The return value of parsehtml is a linked list of variant structures,
with the generic portion described by the following definition:
typedef struct Item Item;
struct Item
{
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Item* next;
int width;
int height;
int ascent;
int anchorid;
int state;
Genattr* genattr;
int tag;
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};
The field next points to the successor in the linked list of items,
while width, height, and ascent are intended for use by the caller
as part of the layout process. Anchorid, if non-zero, gives the
integer id assigned by the parser to the anchor that this item
is in (see section Anchors). State is a collection of flags and
values described as follows:
enum
{
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IFbrk = 0x80000000,
IFbrksp = 0x40000000,
IFnobrk = 0x20000000,
IFcleft = 0x10000000,
IFcright = 0x08000000,
IFwrap = 0x04000000,
IFhang = 0x02000000,
IFrjust = 0x01000000,
IFcjust = 0x00800000,
IFsmap = 0x00400000,
IFindentshift = 8,
IFindentmask = (255<<IFindentshift),
IFhangmask = 255
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};
IFbrk is set if a break is to be forced before placing this item.
IFbrksp is set if a 1 line space should be added to the break
(in which case IFbrk is also set). IFnobrk is set if a break is
not permitted before the item. IFcleft is set if left floats should
be cleared (that is, if the list of pending left floats should
be placed) before this item is placed, and
IFcright is set for right floats. In both cases, IFbrk is also
set. IFwrap is set if the line containing this item is allowed
to wrap. IFhang is set if this item hangs into the left indent.
IFrjust is set if the line containing this item should be right
justified, and IFcjust is set for center justified lines. IFsmap
is used to indicate that an image is a server-
side map. The low 8 bits, represented by IFhangmask, indicate
the current hang into left indent, in tenths of a tabstop. The
next 8 bits, represented by IFindentmask and IFindentshift, indicate
the current indent in tab stops.
The field genattr is an optional pointer to an auxiliary structure,
described in the section Generic Attributes.
Finally, tag describes which variant type this item has. It can
have one of the values Itexttag, Iruletag, Iimagetag, Iformfieldtag,
Itabletag, Ifloattag or Ispacertag. For each of these values,
there is an additional structure defined, which includes Item
as an unnamed initial substructure, and then defines additional
fields.
Items of type Itexttag represent a piece of text, using the following
structure:
struct Itext
{
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Item;
Rune* s;
int fnt;
int fg;
uchar voff;
uchar ul;
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};
Here s is a null-terminated Unicode string of the actual characters
making up this text item, fnt is the font number (described in
the section Font Numbers), and fg is the RGB encoded color for
the text. Voff measures the vertical offset from the baseline;
subtract Voffbias to get the actual value (negative values represent
a displacement down the
page). The field ul is the underline style: ULnone if no underline,
ULunder for conventional underline, and ULmid for strike-through.
Items of type Iruletag represent a horizontal rule, as follows:
struct Irule
{
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Item;
uchar align;
uchar noshade;
int size;
Dimen wspec;
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};
Here align is the alignment specification (described in the corresponding
section), noshade is set if the rule should not be shaded, size
is the height of the rule (as set by the size attribute), and
wspec is the desired width (see section Dimension Specifications).
Items of type Iimagetag describe embedded images, for which the
following structure is defined:
struct Iimage
{
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Item;
Rune* imsrc;
int imwidth;
int imheight;
Rune* altrep;
Map* map;
int ctlid;
uchar align;
uchar hspace;
uchar vspace;
uchar border;
Iimage* nextimage;
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};
Here imsrc is the URL of the image source, imwidth and imheight,
if non-zero, contain the specified width and height for the image,
and altrep is the text to use as an alternative to the image,
if the image is not displayed. Map, if set, points to a structure
describing an associated client-side image map. Ctlid is reserved
for use by the application,
for handling animated images. Align encodes the alignment specification
of the image. Hspace contains the number of pixels to pad the
image with on either side, and Vspace the padding above and below.
Border is the width of the border to draw around the image. Nextimage
points to the next image in the document (the head of this list
is
Docinfo.images).
For items of type Iformfieldtag, the following structure is defined:
struct Iformfield
{
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Item;
Formfield* formfield;
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};
This adds a single field, formfield, which points to a structure
describing a field in a form, described in section Forms.
For items of type Itabletag, the following structure is defined:
struct Itable
{
};
Table points to a structure describing the table, described in
the section Tables.
For items of type Ifloattag, the following structure is defined:
struct Ifloat
{
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Item;
Item* item;
int x;
int y;
uchar side;
uchar infloats;
Ifloat* nextfloat;
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};
The item points to a single item (either a table or an image)
that floats (the text of the document flows around it), and side
indicates the margin that this float sticks to; it is either ALleft
or ALright. X and y are reserved for use by the caller; these
are typically used for the coordinates of the top of the float.
Infloats is used by the caller to keep
track of whether it has placed the float. Nextfloat is used by
the caller to link together all of the floats that it has placed.
For items of type Ispacertag, the following structure is defined:
struct Ispacer
{
};
Spkind encodes the kind of spacer, and may be one of ISPnull (zero
height and width), ISPvline (takes on height and ascent of the
current font), ISPhspace (has the width of a space in the current
font) and ISPgeneral (for all other purposes, such as between
markers and lists).
Generic Attributes
The genattr field of an item, if non-nil, points to a structure
that holds the values of attributes not specific to any particular
item type, as they occur on a wide variety of underlying HTML
tags. The structure is as follows:
typedef struct Genattr Genattr;
struct Genattr
{
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Rune* id;
Rune* class;
Rune* style;
Rune* title;
SEvent* events;
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};
Fields id, class, style and title, when non-nil, contain values
of correspondingly named attributes of the HTML tag associated
with this item. Events is a linked list of events (with corresponding
scripted actions) associated with the item:
typedef struct SEvent SEvent;
struct SEvent
{
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SEvent* next;
int type;
Rune* script;
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};
Here, next points to the next event in the list, type is one of
SEonblur, SEonchange, SEonclick, SEondblclick, SEonfocus, SEonkeypress,
SEonkeyup, SEonload, SEonmousedown, SEonmousemove, SEonmouseout,
SEonmouseover, SEonmouseup, SEonreset, SEonselect, SEonsubmit
or SEonunload, and script is the text of
the associated script.
Dimension Specifications
Some structures include a dimension specification, used where
a number can be followed by a % or a * to indicate percentage
of total or relative weight. This is encoded using the following
structure:
typedef struct Dimen Dimen;
struct Dimen
{
};
Separate kind and spec values are extracted using dimenkind and
dimenspec. Dimenkind returns one of Dnone, Dpixels, Dpercent or
Drelative. Dnone means that no dimension was specified. In all
other cases, dimenspec should be called to find the absolute number
of pixels, the percentage of total, or the relative weight.
Background Specifications
It is possible to set the background of the entire document, and
also for some parts of the document (such as tables). This is
encoded as follows:
typedef struct Background Background;
struct Background
{
};
Image, if non-nil, is the URL of an image to use as the background.
If this is nil, color is used instead, as the RGB value for a
solid fill color.
Alignment Specifications
Certain items have alignment specifiers taken from the following
enumerated type:
enum
{
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ALnone = 0, ALleft, ALcenter, ALright, ALjustify,
ALchar, ALtop, ALmiddle, ALbottom, ALbaseline
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};
These values correspond to the various alignment types named in
the HTML 4.0 standard. If an item has an alignment of ALleft or
ALright, the library automatically encapsulates it inside a float
item.
Tables, and the various rows, columns and cells within them, have
a more complex alignment specification, composed of separate vertical
and horizontal alignments:
typedef struct Align Align;
struct Align
{
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uchar halign;
uchar valign;
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};
Halign can be one of ALnone, ALleft, ALcenter, ALright, ALjustify
or ALchar. Valign can be one of ALnone, ALmiddle, ALbottom, ALtop
or ALbaseline.
Font Numbers
Text items have an associated font number (the fnt field), which
is encoded as style*NumSize+size. Here, style is one of FntR,
FntI, FntB or FntT, for roman, italic, bold and typewriter font
styles, respectively, and size is Tiny, Small, Normal, Large or
Verylarge. The total number of possible font numbers is NumFnt,
and the default font
number is DefFnt (which is roman style, normal size).
Document Info
Global information about an HTML page is stored in the following
structure:
typedef struct Docinfo Docinfo;
struct Docinfo
{
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// stuff from HTTP headers, doc head, and body tag
Rune* src;
Rune* base;
Rune* doctitle;
Background background;
Iimage* backgrounditem;
int text;
int link;
int vlink;
int alink;
int target;
int chset;
int mediatype;
int scripttype;
int hasscripts;
Rune* refresh;
Kidinfo* kidinfo;
int frameid;
// info needed to respond to user actions
Anchor* anchors;
DestAnchor* dests;
Form* forms;
Table* tables;
Map* maps;
Iimage* images;
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};
Src gives the URL of the original source of the document, and
base is the base URL. Doctitle is the document’s title, as set
by a <title> element. Background is as described in the section
Background Specifications, and backgrounditem is set to be an
image item for the document’s background image (if given as a
URL), or else nil. Text
gives the default foregound text color of the document, link the
unvisited hyperlink color, vlink the visited hyperlink color,
and alink the color for highlighting hyperlinks (all in 24-bit
RGB format). Target is the default target frame id. Chset and
mediatype are as for the chset and mtype parameters to parsehtml.
Scripttype is the type of any
scripts contained in the document, and is always TextJavascript.
Hasscripts is set if the document contains any scripts. Scripting
is currently unsupported. Refresh is the contents of a <meta http−equiv=Refresh
...> tag, if any. Kidinfo is set if this document is a frameset
(see section Frames). Frameid is this document’s frame id.
Anchors is a list of hyperlinks contained in the document, and
dests is a list of hyperlink destinations within the page (see
the following section for details). Forms, tables and maps are
lists of the various forms, tables and client-side maps contained
in the document, as described in subsequent sections. Images is
a list of all the image items in the
document.
Anchors
The library builds two lists for all of the <a> elements (anchors)
in a document. Each anchor is assigned a unique anchor id within
the document. For anchors which are hyperlinks (the href attribute
was supplied), the following structure is defined:
typedef struct Anchor Anchor;
struct Anchor
{
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Anchor* next;
int index;
Rune* name;
Rune* href;
int target;
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};
Next points to the next anchor in the list (the head of this list
is Docinfo.anchors). Index is the anchor id; each item within
this hyperlink is tagged with this value in its anchorid field.
Name and href are the values of the correspondingly named attributes
of the anchor (in particular, href is the URL to go to). Target
is the value of the target
attribute (if provided) converted to a frame id.
Destinations within the document (anchors with the name attribute
set) are held in the Docinfo.dests list, using the following structure:
typedef struct DestAnchor DestAnchor;
struct DestAnchor
{
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DestAnchor* next;
int index;
Rune* name;
Item* item;
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};
Next is the next element of the list, index is the anchor id,
name is the value of the name attribute, and item is points to
the item within the parsed document that should be considered
to be the destination.
Forms
Any forms within a document are kept in a list, headed by Docinfo.forms.
The elements of this list are as follows:
typedef struct Form Form;
struct Form
{
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Form* next;
int formid;
Rune* name;
Rune* action;
int target;
int method;
int nfields;
Formfield* fields;
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};
Next points to the next form in the list. Formid is a serial number
for the form within the document. Name is the value of the form’s
name or id attribute. Action is the value of any action attribute.
Target is the value of the target attribute (if any) converted
to a frame target id. Method is one of HGet or HPost. Nfields
is the number of fields in the
form, and fields is a linked list of the actual fields.
The individual fields in a form are described by the following
structure:
typedef struct Formfield Formfield;
struct Formfield
{
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Formfield* next;
int ftype;
int fieldid;
Form* form;
Rune* name;
Rune* value;
int size;
int maxlength;
int rows;
int cols;
uchar flags;
Option* options;
Item* image;
int ctlid;
SEvent* events;
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};
Here, next points to the next field in the list. Ftype is the
type of the field, which can be one of Ftext, Fpassword, Fcheckbox,
Fradio, Fsubmit, Fhidden, Fimage, Freset, Ffile, Fbutton, Fselect
or Ftextarea. Fieldid is a serial number for the field within
the form. Form points back to the form containing this field.
Name, value,
size, maxlength, rows and cols each contain the values of corresponding
attributes of the field, if present. Flags contains per-field
flags, of which FFchecked and FFmultiple are defined. Image is
only used for fields of type Fimage; it points to an image item
containing the image to be displayed. Ctlid is reserved for use
by the caller,
typically to store a unique id of an associated control used to
implement the field. Events is the same as the corresponding field
of the generic attributes associated with the item containing
this field. Options is only used by fields of type Fselect; it
consists of a list of possible options that may be selected for
that field, using the following structure:
typedef struct Option Option;
struct Option
{
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Option* next;
int selected;
Rune* value;
Rune* display;
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};
Next points to the next element of the list. Selected is set if
this option is to be displayed initially. Value is the value to
send when the form is submitted if this option is selected. Display
is the string to display on the screen for this option.
Tables
The library builds a list of all the tables in the document, headed
by Docinfo.tables. Each element of this list has the following
format:
typedef struct Table Table;
struct Table
{
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Table* next;
int tableid;
Tablerow* rows;
int nrow;
Tablecol* cols;
int ncol;
Tablecell* cells;
int ncell;
Tablecell*** grid;
Align align;
Dimen width;
int border;
int cellspacing;
int cellpadding;
Background background;
Item* caption;
uchar caption_place;
Lay* caption_lay;
int totw;
int toth;
int caph;
int availw;
Token* tabletok;
uchar flags;
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};
Next points to the next element in the list of tables. Tableid
is a serial number for the table within the document. Rows is
an array of row specifications (described below) and nrow is the
number of elements in this array. Similarly, cols is an array
of column specifications, and ncol the size of this array. Cells
is a list of all cells within the table
(structure described below) and ncell is the number of elements
in this list. Note that a cell may span multiple rows and/or columns,
thus ncell may be smaller than nrow*ncol. Grid is a two-dimensional
array of cells within the table; the cell at row i and column
j is Table.grid[i][j]. A cell that spans multiple rows and/or
columns will be
referenced by grid multiple times, however it will only occur
once in cells. Align gives the alignment specification for the
entire table, and width gives the requested width as a dimension
specification. Border, cellspacing and cellpadding give the values
of the corresponding attributes for the table, and background
gives the requested
background for the table. Caption is a linked list of items to
be displayed as the caption of the table, either above or below
depending on whether caption_place is ALtop or ALbottom. Most
of the remaining fields are reserved for use by the caller, except
tabletok, which is reserved for internal use. The type Lay is
not defined by the library; the
caller can provide its own definition.
The Tablecol structure is defined for use by the caller. The library
ensures that the correct number of these is allocated, but leaves
them blank. The fields are as follows:
typedef struct Tablecol Tablecol;
struct Tablecol
{
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int width;
Align align;
Point pos;
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};
The rows in the table are specified as follows:
typedef struct Tablerow Tablerow;
struct Tablerow
{
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Tablerow* next;
Tablecell* cells;
int height;
int ascent;
Align align;
Background background;
Point pos;
uchar flags;
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};
Next is only used during parsing; it should be ignored by the
caller. Cells provides a list of all the cells in a row, linked
through their nextinrow fields (see below). Height, ascent and
pos are reserved for use by the caller. Align is the alignment
specification for the row, and background is the background to
use, if specified. Flags is used by
the parser; ignore this field.
The individual cells of the table are described as follows:
typedef struct Tablecell Tablecell;
struct Tablecell
{
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Tablecell* next;
Tablecell* nextinrow;
int cellid;
Item* content;
Lay* lay;
int rowspan;
int colspan;
Align align;
uchar flags;
Dimen wspec;
int hspec;
Background background;
int minw;
int maxw;
int ascent;
int row;
int col;
Point pos;
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};
Next is used to link together the list of all cells within a table
(Table.cells), whereas nextinrow is used to link together all
the cells within a single row (Tablerow.cells). Cellid provides
a serial number for the cell within the table. Content is a linked
list of the items to be laid out within the cell. Lay is reserved
for the user to describe how
these items have been laid out. Rowspan and colspan are the number
of rows and columns spanned by this cell, respectively. Align
is the alignment specification for the cell. Flags is some combination
of TFparsing, TFnowrap and TFisth or’d together. Here TFparsing
is used internally by the parser, and should be ignored. TFnowrap
means that the contents of the cell should not be wrapped if they
don’t fit the available width, rather, the table should be expanded
if need be (this is set when the nowrap attribute is supplied).
TFisth means that the cell was created by the <th> element (rather
than the <td> element), indicating that it is a header cell rather
than a data cell. Wspec
provides a suggested width as a dimension specification, and hspec
provides a suggested height in pixels. Background gives a background
specification for the individual cell. Minw, maxw, ascent and
pos are reserved for use by the caller during layout. Row and
col give the indices of the row and column of the top left-hand
corner of the cell within
the table grid.
Client-side Maps
The library builds a list of client-side maps, headed by Docinfo.maps,
and having the following structure:
typedef struct Map Map;
struct Map
{
| |
Map* next;
Rune* name;
Area* areas;
|
};
Next points to the next element in the list, name is the name
of the map (use to bind it to an image), and areas is a list of
the areas within the image that comprise the map, using the following
structure:
typedef struct Area Area;
struct Area
{
| |
Area* next;
int shape;
Rune* href;
int target;
Dimen* coords;
int ncoords;
|
};
Next points to the next element in the map’s list of areas. Shape
describes the shape of the area, and is one of SHrect, SHcircle
or SHpoly. Href is the URL associated with this area in its role
as a hypertext link, and target is the target frame it should
be loaded in. Coords is an array of coordinates for the shape,
and ncoords is the size of
this array (number of elements).
Frames
If the Docinfo.kidinfo field is set, the document is a frameset.
In this case, it is typical for parsehtml to return nil, as a
document which is a frameset should have no actual items that
need to be laid out (such will appear only in subsidiary documents).
It is possible that items will be returned by a malformed document;
the caller should check for this
and free any such items.
The Kidinfo structure itself reflects the fact that framesets
can be nested within a document. If is defined as follows:
typedef struct Kidinfo Kidinfo;
struct Kidinfo
{
| |
Kidinfo* next;
int isframeset;
// fields for "frame"
Rune* src;
Rune* name;
int marginw;
int marginh;
int framebd;
int flags;
// fields for "frameset"
Dimen* rows;
int nrows;
Dimen* cols;
int ncols;
Kidinfo* kidinfos;
Kidinfo* nextframeset;
|
};
Next is only used if this structure is part of a containing frameset;
it points to the next element in the list of children of that
frameset. Isframeset is set when this structure represents a frameset;
if clear, it is an individual frame.
Some fields are used only for framesets. Rows is an array of dimension
specifications for rows in the frameset, and nrows is the length
of this array. Cols is the corresponding array for columns, of
length ncols. Kidinfos points to a list of components contained
within this frameset, each of which may be a frameset or a frame.
Nextframeset is
only used during parsing, and should be ignored.
The remaining fields are used if the structure describes a frame,
not a frameset. Src provides the URL for the document that should
be initially loaded into this frame. Note that this may be a relative
URL, in which case it should be interpretted using the containing
document’s URL as the base. Name gives the name of the frame,
typically supplied via a
name attribute in the HTML. If no name was given, the library
allocates one. Marginw, marginh and framebd are the values of
the marginwidth, marginheight and frameborder attributes, respectively.
Flags can contain some combination of the following: FRnoresize
(the frame had the noresize attribute set, and the user should
not be allowed to
resize it), FRnoscroll (the frame should not have any scroll bars),
FRhscroll (the frame should have a horizontal scroll bar), FRvscroll
(the frame should have a vertical scroll bar), FRhscrollauto (the
frame should be automatically given a horizontal scroll bar if
its contents would not otherwise fit), and FRvscrollauto (the
frame gets a vertical
scrollbar only if required).
|
SOURCE
SEE ALSO
| |
fmt(1)
W3C World Wide Web Consortium, “HTML 4.01 Specification”.
|
BUGS
| |
The entire HTML document must be loaded into memory before any
of it can be parsed.
|
|
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